Statistical Skills AQA AS Level Geography (unit 2)

The AQA specification requires you to know

 • measures of central tendency – mean, mode, 


• measures of dispersion – interquartile range and 

standard deviation

• Spearman’s rank correlation test

Here is a simple explanation of them all.

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  • Created by: Annie
  • Created on: 28-05-12 10:40
Preview of Statistical Skills AQA AS Level Geography (unit 2)

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Geography Skills Paper
Interquartile Range
Step 1: Put the numbers in order
Step 2: Find the median (How to find a median)
Step 3: Find Q1 and Q3
Q1 can be thought of as a median in the lower half of the data, and Q3 can be thought of as
a median for the upper half of data.
(1,2,5,6,7), 9, ( 12,15,18,19,27). Q1=5 and Q3=18.
Step 4:Subtract Q1 from Q3 to find the interquartile range.
Standard deviation
Column 2 here stands for the deviant (rainfall (x) ­ the average rainfall)
Column 3 here stands for the deviant squared (rainfal (x) ­ the average rainfall) SQUARED.
Standard deviation describes how spread out the data is. If the data all lies close to the mean,
then the standard deviation will be small, while if the data is spread out over a large range of
values, will be large.
Mode: result that occurs most frequently.
Mean: Sum of all the results/ the number of results.

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Median: Put them in order then it is `the middle value': if there are an even number of values
then take the middle two values and divide them by 2.
Spearman's Rank: Spearman's rank correlation coefficient allows you to identify easily the
strength of correlation within a data set of two variables and whether the correlation is positive
or negative. It is for comparing data groups.
Eg. Here you have 2 data sets:
1.…read more

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Work out the differences between the ranks (if rank 1=1 and rank 2=2 then the difference
would be 1).
5. Square the differences.
6. Add up all results in the d squared column: eg. This would become
7. Put this result into the Spearmans rank coefficient formula e.g.
8. replace the `n's with the number of results you have taken e.g.…read more

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Interperet your results: your result WILL vary between 1 and 1 if you have done you
calculation correctly:
Close to 1= Negative correlation
Close to 0= No linear correlation
Close to 1= Positive correlation…read more


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